Thank you for reporting back! Have you found a source for a new high/low detection switch? There is another member on this forum with a problem that may be caused by his high/low switch. I Googled it, but only found suppliers in the UK as RoversNorth's site was being difficult.

It also looks like your symptoms on the shifting might help prove something he had read about the ECU mapping of shift points being different from high to low range.

 

I repaired mine and then heat shank it with a little dialetric for good measure. it should be pretty water tight. If i run into issue later I will just order a new one from the dealer and replace. it is as easy as dropping your front shaft at the TC and hanging it out of the way.
Detection switch is right there above and to the left of the CDL nipple.

cheers